Method of manufacturing ceramic led packages

ABSTRACT

Methods of fabricating a light-emitting device are provided. A light-emitting device can be formed from bonding a lens including a plug and a cap to an LED package including a socket configured to receive the plug. The lens can be fabricated using an injection mold formed from a well secured to the LED package and injecting a material into the injection mold to cure into a shape of the lens. The lens can also be fabricated using a blank about the shape of the lens and machining the blank to produce the plug and the cap of the lens. The lens can be bonded to the LED package using a convex bead of adhesive deposited on the surface of the LED package and spreading the adhesive between the lens and the LED package.

CROSS-REFERENCES TO RELATED APPLICATIONS

The application is a divisional application of U.S. patent applicationSer. No. 11/796,240, filed on Apr. 27, 2007 entitled “LED Packages withMushroom Shaped Lenses and Methods of Manufacturing LED Light-EmittingDevices,” which is a continuation in part of U.S. patent applicationSer. No. 11/260,101, filed on Oct. 26, 2005 entitled “Method ofManufacturing Ceramic LED Packages,” now U.S. Pat. No. 7,670,872, whichin turn claims the benefit of U.S. Provisional Patent Application No.60/623,266 entitled “1-5 Watt and Higher LED Packages,” U.S. ProvisionalPatent Application No. 60/623,171 entitled “3-10 Watt and Higher LEDPackages,” and U.S. Provisional Patent Application No. 60/623,260entitled “5-15 Watt and Higher LED Packages,” each filed on Oct. 29,2004. The application is related to U.S. patent application Ser. No.11/259,818 entitled “LED Package with Structure and Materials for HighHeat Dissipation,” now U.S. Pat. No. 7,772,609, and U.S. patentapplication Ser. No. 11/259,842 entitled “High Power LED Package withUniversal Bonding Pads and Interconnect Arrangement,” now U.S. Pat. No.7,473,933, both filed on Oct. 26, 2005. The application is also relatedto U.S. patent application Ser. No. 11/036,559 filed on Jan. 13, 2005and entitled “Light Emitting Device with a Thermal Insulating andRefractive Index Matching Material,” now U.S. Pat. No. 8,134,292. Allapplications noted above are incorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present disclosure relates generally to light emitting diodes andmore particularly to packages for high-power LEDs.

2. Description of the Prior Art

A light emitting diode (LED) is a semiconductor device that produceslight when an electric current is passed therethrough. LEDs have manyadvantages over other lighting sources including compactness, very lowweight, inexpensive and simple manufacturing, freedom from burn-outproblems, high vibration resistance, and an ability to endure frequentrepetitive operations. In addition to having widespread applications forelectronic products as indicator lights and so forth, LEDs also havebecome an important alternative light source for various applicationswhere incandescent and fluorescent lamps have traditionallypredominated.

Using phosphors as light “converters,” LEDs can also serve to producewhite light. In a typical LED-based white light producing device, amonochromatic LED is encapsulated by a transparent material containingappropriate phosphors. In some systems, an LED that produces amonochromatic visible light is encapsulated by a material containing acompensatory phosphor. The wavelength(s) of the light emitted from thecompensatory phosphor is compensatory to the wavelength of the lightemitted by the LED such that the wavelengths from the LED and thecompensatory phosphor mix together to produce white light. For instance,a blue LED-based white light source produces white light by using a bluelight LED and a phosphor that emits a yellowish light when excited bythe blue light emitted from the LED. In these devices the amount of thephosphor in the transparent material is carefully controlled such thatonly a fraction of the blue light is absorbed by the phosphor while theremainder passes unabsorbed. The yellowish light and the unabsorbed bluelight mix to produce white light. Another exemplary scheme uses an LEDthat produces light outside of the visible spectrum, such as ultraviolet(UV) light, together with a mixture of phosphors capable of producingeither red, green, or blue light when excited. In this scheme, the lightemitted by the LED only serves to excite the phosphors and does notcontribute to the final color balance.

Recent advances in semiconductor technology have made it possible tomanufacture high-power LEDs that produce light at selected wavelengthsacross the visible spectrum (400-700 nm). Such high-power LEDs can havereliability and cost advantages over existing technologies such asincandescent lamps, arc lamps, and fluorescent lamps in many lightingapplications. High-power LEDs also offer advantages for design of nextgeneration color display technologies such as active matrix thin filmtransistor liquid crystal displays (TFTLCDs) in applications such asconsumer computer and television monitors, projection TVs, and largeadvertising displays.

Although high-power LED devices have been manufactured, their widespreaduse has been limited because of a lack of suitable packages for theLEDs. Current LED packages cannot handle the high-power density of LEDchips. In particular, prior art packages provide inadequate heatdissipation away from the LED dies. Inadequate heat dissipation limitsthe minimum size of the package and therefore the density of LEDs perunit area in the device. One measure of how efficiently a packagedissipates heat is the temperature rise across the package for a giveninput electrical power. This measure is generally in the range of 15 to20 degrees centigrade per watt (° C./W) from the junction to the case incurrent LED packages, usually too high to provide adequate heatdissipation for an LED package having a power higher than 1 watt.

Without sufficient heat dissipation, devices incorporating high-poweredLEDs can run very hot. Light output, LED efficiency, and LED life, areeach dependent on the LED die junction temperature. Inadequate heatdissipation will cause the LED Die to operate at a higher temperatureand therefore limits the performance of the LED die when the LED die iscapable of operating at a power level exceeding the limits of thepackage. Insufficient heat dissipation by an LED package can cause theLED device to fail at an early stage or render it too hot to use safely.

Even under less severe conditions, inadequate heat conduction for an LEDpackage may result in poor thermal stability of the phosphors, as wellas encapsulation and lens materials, in those devices that employphosphors. Specifically, exposure to high temperatures for extendedperiods tends to alter the chemical and physical properties of suchphosphors, encapsulation, and lens materials, causing performancedeterioration. For instance, the light conversion efficiency can declineand the wavelength of output light can shift, both altering the balanceof the light mixture and potentially diminishing the intensity of theoverall output. For example, currently available phosphors are oftenbased on oxide or sulfide host lattices including certain rare earthions. Under prolonged high temperature conditions, these latticesdecompose and change their optical behavior. Other problems commonlyfound with LED-based white light sources are transient color changes anduneven color distributions, both caused by temperature gradients in thephosphor-containing material and degradation of the encapsulation andlens materials. Such behaviors often create an unsatisfactoryillumination. The above-mentioned thermal problems worsen withincreasing temperature and therefore are particularly severe for devicesthat incorporate high-power LEDs with phosphors.

Attempts have been made in current LED packages to alleviate the aboveproblem. One example is to directly attach an LED die to a top surfaceof a metal heat slug such as a copper plate. The copper plate serves tospread the heat and to make electrical connections with the LED die.This design limits the selection of materials for the heat slug becausethe design relies at least partially on the conductive nature of thecopper for making the conductive contacts between the LED die and thetop surface of the copper heat slug. The use of copper heat slugs alsohas other limitations, such as a substantial mismatch between thecoefficients of thermal expansion (CTE) of the LED die material and thecopper onto which the LED die is attached. A large CTE mismatch cancreate high stresses upon heating a cooling at bonded interfaces. Cracksthat form at these interfaces then render the LED package unreliable. Inaddition, the above design is relatively expensive and difficult tomanufacture.

Other problems associated with LED packages relate to how lenses areattached. Typically, a layer of transparent adhesive is used to securethe lens to the package. Frequently, air bubbles form in the adhesive.The air bubbles increase internal reflections of the light in theadhesive layer, reducing the amount of light transmitted through theadhesive layer. Additionally, the lens can also become inadvertentlydetached from the package. This can happen when the lens experiences ashear force, for example a side impact that “pops” the lens off thepackage.

Given the importance of LEDs as light sources, particularly high-powerLEDs, there is a need for improved LED packaging methods and materialsto alleviate the above-identified problems by providing better thermalperformance (e.g., improved thermal resistance from junction to case)and higher reliabilities (e.g., lower stresses in packaging materials).Such packaging methods and materials will allow LEDs to produce higheroptical performance (Lumens/package) from a smaller package or footprinthigher optical performance any light source applications.

BRIEF SUMMARY OF THE INVENTION

The present disclosure addresses the above problems by providing methodsfor forming LED packages and light emitting devices. According to anembodiment of the invention, a method for forming an LED packagecomprises forming a panel, defining a grid on a surface of the panel,and separating the LED package from the panel by breaking the panelalong lines of the grid. Forming the panel includes forming a top layer,an intermediate body layer, and a thermally conducting layer, andbonding the intermediate body layer between the top and thermallyconducting layers. Forming the panel can further include forming analignment layer, and these embodiments also include bonding thealignment layer to the top layer opposite the intermediate layer.

In some embodiments of the method of forming the LED package forming thethermally conducting layer includes preparing a sheet of AlN. Formingthe thermally conducting layer can also include forming a sheet with asquare array of vias disposed therethrough. Forming the thermallyconducting layer can further include forming a metallization pattern ona top surface of the thermally conducting layer, and in theseembodiments bonding the intermediate body layer includes bonding theintermediate body layer to the top surface of the thermally conductinglayer. In some of these embodiments forming the thermally conductinglayer further includes forming a metallization pattern on a bottomsurface of the thermally conducting layer.

In some embodiments of the method of forming the LED package forming theintermediate body layer includes preparing a sheet of AlN. Forming theintermediate body layer can also include forming a sheet with a squarearray of vias disposed therethrough and an aperture disposed within eachsquare defined by the array. Likewise, forming the top body layer caninclude preparing a sheet of AlN, and can also include forming a sheetwith a square array of vias disposed therethrough and an aperturedisposed within each square defined by the array. In some of theselatter embodiments the aperture within each square has an inclinedsidewall, and forming the top body layer can further include metallizinga sidewall of the aperture within each square. Forming the top bodylayer can further include forming a metallization pattern on a topsurface of the top body layer, and in these embodiments bonding theintermediate body layer between the top and thermally conducting layersincludes bonding the intermediate body layer to a bottom surface of thetop body layer.

In other embodiments of the method of forming the LED package bondingthe intermediate body layer between the top and thermally conductinglayers includes co-firing. Bonding the intermediate body layer betweenthe top and thermally conducting layers can also include aligning asquare array of vias defined in each of the layers. The step of bondingthe intermediate body layer between the top and thermally conductinglayers can alternatively include applying an adhesive between two of thelayers.

In still other embodiments of the method of forming the LED packageforming the intermediate body layer includes forming a metal sheet witha square array of vias disposed therethrough an aperture disposed withineach square defined by the array. In these embodiments bonding theintermediate body layer between the top and thermally conducting layersincludes applying an electrically insulating adhesive between theintermediate body layer and the thermally conducting layer.

In yet other embodiments of the method of forming the LED packagedefining the grid on the surface of the panel includes scribing snaplines on the surface of the panel. Where one of the top, intermediatebody, or thermally conducting layers is a non-ceramic layer, the step offorming the non-ceramic layer includes defining a grid thereon. In someof these embodiments defining the grid on the surface of the panelincludes aligning the grid on the surface of the panel with the griddefined on the non-ceramic layer.

In still other embodiments of the method of forming the LED packageforming the panel includes forming a square array of vias disposedtherethrough. In some of these embodiments defining the grid on thesurface of the panel includes scribing snap lines on the surface of thepanel that intersect the vias. In these embodiments the method canfurther include plating metal into the vias.

According to another embodiment of the invention, a method for forming alight emitting device comprises forming a panel having a square array ofvias disposed therethrough and a cavity disposed within each squaredefined by the array, defining a grid on a surface of the panel, bondingan LED die to a floor of each cavity, and separating the light emittingdevice from the panel by breaking the panel along lines of the grid. Insome embodiments the method further comprises encapsulating each LEDdie. In some of these embodiments encapsulating each LED die includesforming a thermally insulating layer over each LED die, and forming aluminescent layer over each thermally insulating layer. Some embodimentsof the method further comprise forming a lens over the LED die. In someof these embodiments forming the lens includes injection molding orprinting with masks.

According to another embodiment of the invention, a light-emittingdevice comprises a package and a lens. The package includes alight-emitting side, an encapsulated LED configured to emit light towardthe light-emitting side of the package, and a socket including asidewall and a bottom surface, the socket disposed on the light-emittingside of the package. The lens includes a cap and a plug, where the plugis disposed within the socket. In some embodiments, the shape of thelens comprises a mushroom shape. An angle defined between the sidewalland the bottom surface of the socket can be between about 45 degrees toabout 140 degrees. Likewise, an angle defined between a sidewall of theplug and a lower surface of the lens can also be between about 45degrees to about 140 degrees. The light-emitting device can also includean adhesive layer, such as silicone, disposed between the lens and thepackage.

According to another embodiment of the invention, a method offabricating a light-emitting device is provided. The exemplary methodcomprises providing a lens including a plug and a cap, and providing apackage including an encapsulated LED configured to emit light toward alight-emitting side of the package, and a socket disposed on thelight-emitting side of the package. The method further comprisesdepositing an adhesive within the socket, and attaching the lens to thelight-emitting side of the package, such that the plug is disposedwithin the socket. In some embodiments, providing the lens comprisesmachining a lens blank, such as by turning the lens blank, to form theplug of the lens.

Another exemplary method of fabricating a light-emitting device alsocomprises providing a package including an encapsulated LED configuredto emit light toward a light-emitting side of the package, and a socketdisposed on the light-emitting side of the package. In this exemplarymethod, a mold defining a shape of a cap is placed over the socket,material is flowed into a space formed by the mold and the socket, andthe material is cured to form the lens in place.

Still another exemplary method is directed to attaching an LED lens toan LED package to form a light-emitting device. This exemplary methodcomprises introducing a bead of adhesive, such as silicone, having aconvex surface and a viscosity of about 2000 to 4000 centipoise onto asurface of the LED package, contacting a point on the convex surface ofthe bead of adhesive with a surface of the LED lens, and spreading theadhesive between the surface of the LED package and the surface of theLED lens. In some embodiments, the contacted point on the convex surfaceof the bead of adhesive is at about an apex of the convex surface of thebead of adhesive. In various embodiments a width of the bead of adhesiveis between about 30 percent to about 55 percent of a length of thesurface of the LED package, and a height of the bead of adhesive isbetween about 20 percent to about 35 percent of a width of the bead ofadhesive.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an LED die bonded to an exemplary LEDpackage according to an embodiment of the present disclosure.

FIG. 2 is a cross-sectional view of an exemplary embodiment of the LEDpackage of the present disclosure.

FIG. 3 is a top view of an exemplary LED package of the presentdisclosure.

FIGS. 4A and 4B are exemplary metallization patterns for a top surfaceof a thermally conducting layer of an LED package according toembodiments of the present disclosure.

FIG. 5 is an exemplary metallization pattern for the bottom surface of athermally conducting layer of an LED package according to an embodimentof the present disclosure.

FIGS. 6A-6C are cross-sectional views of several exemplary embodimentsof an LED package of the present disclosure.

FIG. 7 is a top view of an LED package in accordance with anotherembodiment of the present disclosure.

FIG. 8 is a top view of a plurality of LED packages manufactured inparallel during an exemplary embodiment of a fabrication process.

FIG. 9 is a flowchart for a method according to an exemplary embodimentof the invention.

FIGS. 10 and 11 show cross-sectional views of an LED package and a lensin accordance with an embodiment of the present disclosure.

FIG. 12 is a cross-sectional view of an LED package and a lens prior toassembly in accordance with another embodiment of the presentdisclosure.

FIG. 13 is a cross-sectional view of the lens and LED package of FIG. 12assembled, in accordance with another embodiment of the presentdisclosure.

FIG. 14 is a cross-sectional view of an LED package and a lens prior toassembly in accordance with another embodiment of the presentdisclosure.

FIG. 15 is a cross-sectional view of the lens and LED package of FIG. 14assembled, in accordance with another embodiment of the presentdisclosure.

FIGS. 16-19 illustrate successive stages of bonding a lens to an LEDpackage using an adhesive, in accordance with an embodiment of thepresent disclosure.

FIGS. 20-21 illustrate successive steps in fabricating a lens using aninjection mold in accordance with an embodiment of the presentdisclosure.

FIG. 22 is a cross-sectional view of an exemplary embodiment of a lensblank of the present disclosure.

FIG. 23 is a bottom plan view of the lens blank of FIG. 22, inaccordance with an embodiment of the present disclosure.

FIG. 24 is a side elevation of a lens machined from the lens blank ofFIG. 22, in accordance with an embodiment of the present disclosure.

FIG. 25 is a bottom plan view of the lens of FIG. 24, in accordance withanother embodiment of the present disclosure.

FIG. 26 is a bottom plan view of the lens of FIG. 24, in accordance withanother embodiment of the present disclosure.

FIG. 27 is a flowchart for a method according to an exemplary embodimentof the invention.

FIG. 28 is a flowchart for a method according to an exemplary embodimentof the invention.

FIG. 29 is a flowchart for a method according to an exemplary embodimentof the invention.

FIG. 30 is a flowchart for a method according to an exemplary embodimentof the invention.

DETAILED DESCRIPTION OF THE INVENTION

The present disclosure provides LED packages with structures andmaterials that provide higher heat dissipation than presently available.A further benefit of the present invention is improved matching of thecoefficients of thermal expansion (CTES) of the LED dies and thematerials to which they are bonded for higher reliability. Due to theimproved heat conduction, the packages of the present invention allowhigh-power LEDs to operate at full capacity. Improved heat conductionalso allows for both smaller packages and devices within which packagesare placed more closely together.

One measure of how efficiently a package dissipates heat is thetemperature rise across the package. Using this measure, in currenthigh-power LED packages the thermal resistance from the junction to thecase is generally in the range of 15 to 20° C./W. By comparison, anexemplary embodiment of the present disclosure has a lower thermalresistance of only about 6° C./W or 3° C./W for a four LED dice package.Therefore, the present disclosure enables LED devices for newapplications in both high temperature environments (such as in anautomobile engine compartment) and also in environments that cannotaccommodate high temperature components (such as a dental curing lightfor use in a patient's mouth).

Accordingly, exemplary packages for high-power LEDs according to thepresent disclosure have the following features: 1) They offer higherperformance by enabling 50% or greater luminosity per LED die ascompared to prior art packages; 2) they provide a high thermalconductivity path to conduct heat away from LED dies; 3) they redirectlight emitted at low solid angles (tangential light) into directionsmore nearly perpendicular to the surface of the LED die; and 4) theyprovide a material layer, for bonding to the LED die, having a CTE thatis closely matched to the CTE of the LED die to minimize interfacialstresses and improve reliability.

The present disclosure provides embodiments for a package for a singlehigh-power LED die in the 1 to 7 watt output power range that providesthe desirable features discussed above. The present disclosure alsoprovides embodiments to stabilize the wavelength (i.e., color) of LEDdies. In the case of white LED applications, the present disclosureprovides embodiments for improving white light LED efficiency.

The present disclosure also provides embodiments for a package formultiple high-power LED dies with a combined output in the 1 to 15 wattoutput power range. These packages have very small form factors and canbe fabricated at low cost. The small form factors enable the design oflight source optics with more compact sizes. Therefore, the presentinvention enables a new class of high-power LED-based light source anddisplay applications to emerge.

The packages of the present invention can be used with LED devices thatoperate over the range of wavelengths from ultraviolet (UV) to Infrared(IR) which covers the range from 200 to 2000 nanometers. Further,packages of the present invention can include bonding pads configured toaccommodate any of a number of different LED die designs that arepresently available in the market. The present disclosure, in someembodiments, also provides a versatile package design whereby thethermal and electrical paths are separated. In this way, the package canbe attached to a heat sink of a circuit board using either a thermallyand electrically conductive epoxy or solder, or a thermally conductiveand electrically non-conductive epoxy.

FIG. 1 is a perspective view of an exemplary LED package 100 accordingto an embodiment of the invention. To form a light emitting device, anLED die 110 is bonded to the LED package 100 as shown. The LED package100 comprises a body 120 having a cavity 130 extending downward from atop surface 140 thereof. The cavity 130 includes a floor 150 for bondingto the LED die 110. In some embodiments, the LED package 100 has asquare footprint enabling multiple light emitting devices to be denselyarranged in a square array. The LED package 100 is intended primarilyfor LED dies that produce 1-5 watts of power, but is not limitedthereto.

In the embodiment shown in FIG. 1, a sidewall 160 of the cavity 130 isinclined at an angle so that the cavity 130 takes the shape of aninverted and truncated cone. The sidewall can also be vertical, ornearly so. In some embodiments the sidewall 160 of the cavity 130 isinclined at a 45° angle. Preferably, the sidewall 160 is highlyreflective at a wavelength emitted by the LED die 110. This can beachieved, for example, with a coating of a highly reflective materialsuch as silver, though other materials can be used, depending on thewavelength of the light produced by the LED die 110. Thus, the sidewall160 can serve to redirect light emitted from the edges of the LED die110. The light from the edges of the LED die 110 is redirected in adirection perpendicular to a top surface of the LED die 110 so that thelight emitted from the side surfaces of the LED die 110 adds to thelight emitted from the top surface of the LED die 110. In otherembodiments the sidewall 160 takes a parabolic shape to better focus theredirected light.

FIG. 2 is a cross-sectional view of one exemplary embodiment of an LEDpackage 200 of the present disclosure. It can be seen from FIG. 2 thatthe LED package 200 comprises three layers (embodiments with four layersare described elsewhere herein) designated from top to bottom as a topbody layer 210, an intermediate body layer 220 and a thermal conductionlayer 230. The thermal conduction layer 230 has a bottom surface 235. ALED die 240 can be bonded to a top surface of thermal conduction layer230 within a cavity 250 formed through layers 210 and 220. A thicknessof intermediate body layer 220 is designed to be approximately the sameas a thickness of a die attach layer 245 that bonds the LED die 240 tothe thermal conduction layer 230. Also, in some embodiments ametallization layer on a sidewall 255 of the top body layer 210 extendsfrom a top rim 260 at a top surface 280 of the top layer 210 to a bottomrim 270 near a bottom surface of the top body layer 210.

FIG. 3 is a top view of the exemplary LED package 200 of FIG. 2. The toprim 260 and the bottom rim 270 correspond to the outer diameter and theinner diameter of the cavity 250 and are represented by two circles 260and 270, respectively. It can be seen that the LED die 240 is positionedwithin the inner diameter 270. This embodiment also includes partialvias 290, 292, 294, and 296, one at each of the four corners of the LEDpackage 200. The partial vias 290, 292, 294, and 296 are metallized, insome embodiments, to serve as electrical paths.

The thermal conduction layer 230 includes a thermally conductivematerial, which preferably has a thermal conductivity greater than about14 W/m° K, and more preferably has a thermal conductivity greater than150 W/m° K. Depending on applications, power density, desired packagesize and thickness of the several layers, a variety of thermallyconductive materials can be used to form the thermal conduction layer230. Such materials include, but are not limited to, aluminum nitride(AlN), alumina (Al₂O₃), Alloy 42, copper (Cu), copper-tungsten (Cu/W)alloy, aluminum silicon carbide, diamond, graphite, and beryllium oxide.In addition to thermal conductivity, the coefficient of thermalexpansion (CTE), the fracture toughness, Young's modulus, and cost areother parameters to be considered in selecting the material for thethermal conduction layer 230.

Matching the CTE of the thermally conductive material with that of theLED die reduces interfacial stresses and therefore improves reliability.Preferably, the CTE of the thermally conductive material should be lessthan 15 parts per million per degree centigrade (ppm/° C.) in order tomore closely match the CTE of typical LED die materials such as silicon.The mismatch in the CTEs between the LED package and the LED dieaccording to embodiments of the present disclosure is about 4.7:3,whereas for prior art packages the best ratios are about 17:3. Improvedheat dissipation allows packages of the present disclosure to have asmaller footprint and to be thinner than prior art packages. Anexemplary embodiment of the present disclosure has dimensions of 4.4mm×4.4 mm×0.9 mm vs. prior art packages that measure 14 mm×7 mm×2.5 mm.

The thermal conduction layer 230, with the help of layers 210 and 220 insome embodiments, dissipates much of the heat generated by the LED 240.For applications that demand the highest thermal dissipationcapabilities, each of the three layers 210, 220, and 230 compriseceramic AlN. AlN is desirable because it combines high thermalconductivity with a CTE that is very similar to that of LED substratematerials, such as SiC, sapphire, or silicon, the material from whichsolid-state LEDs are most frequently fabricated. However, Al₂O₃ can alsobe used for these layers for other applications. For some applications,thermal conduction layer 230 is made from either AlN or Al₂O₃ whilelayers 210 and 220 are made of other suitable materials includingplastics and metals such as copper, aluminum, and Alloy 42. For someapplications it is desirable to use the thermal conduction layer 230 asthe primary thermal conduction path away from the LED die 240 in orderto prevent heat from being directed towards the top of the package 200.For example, it may be desirable to keep the top of the light emittingdevice cool to the touch.

It will be appreciated that the package 200 does not need to be formedfrom three layers as illustrated by FIG. 2; more or fewer layers alsocan be used. For example, an embodiment with four layers is alsodescribed herein. Ceramic processing techniques can also be used to formthe body as an integral unit. However, a layered configuration isdesirable for the ease of fabrication. For some applications withsecondary lenses, layers 210 and 220 are optional.

It will also be appreciated that heat produced by the LED die 240 isdissipated from the package 200 primarily through the thermal conductionlayer 230. Consequently, layer 230 preferably has a thickness that isoptimized for thermal conductivity therethrough. It has been found thatfor a given material, the thermal conductivity decreases if layer 230 iseither too thin or too thick and, accordingly, there is an optimalthickness for optimal thermal conductivity. In the embodiment where AlNceramic is used for a thermal conduction layer 230, the optimalthickness of layer 230 is in a range of 0.2 mm to 0.4 mm, and ideallyabout 0.3 mm.

It will be appreciated that the LED package 200 may be further attachedto a heat sink (not shown) along the bottom surface 235. In addition, tooptimize heat dissipation from the package 200 to the heat sink, the dieattach layer 245 is preferably also thermally conductive. In the presentdisclosure, for a thin layer to be characterized as being thermallyconductive, the material of the layer should have a thermal conductivityof at least 0.5 W/m° K, and ideally about 50 W/m° K.

In some embodiments, the thermal conductivity of the die attach layer245 is desirably at least 1 W/m° K. The die attach layer 245 cancomprise, for example, an electrically conductive epoxy, a solder, athermally conductive and electrically non-conductive epoxy, or anano-carbon-fiber filled adhesive. In some embodiments as discussedbelow, where the LED die 240 needs to make an electrical connection withthe thermal conduction layer 230 through a central pad, the die attachlayer 245 is also electrically conductive. In this disclosure, a thinlayer material is considered to be electrically conductive if it has avolume resistivity less than 1×10⁻² ohm-meter. A material for anelectrically conductive die attach layer 245 desirably has a volumeresistivity less than 1×10⁻⁴ ohm-meter.

The thermal conduction layer 230, in accordance with the presentdisclosure, may be either electrically conductive or electricallynonconductive. As described below, where the thermal conduction layer230 is electrically nonconductive, the present disclosure uses ametallization pattern for the top surface of the thermal conductionlayer 230 to provide necessary electrical contacts. This unique designmakes it possible to fabricate the thermal conduction layer 230 fromthermally conductive materials that are not electrically conductive,such as ceramics. Electrically nonconductive materials haveconventionally been considered unsuitable for making heat slugs.

FIG. 4A illustrates an exemplary metallization pattern for the topsurface of thermal conduction layer 230 of the LED package 200 of FIGS.2 and 3. It can be seen that a generally square central pad 410 isconnected by a trace 420 to one of the four partial vias (290, 292, 294,and 296), and partial via 294 particularly in FIG. 4A. Nickel andtungsten are exemplary metals for the metallization. The bottom surfaceof the LED die 240 is bonded, for example by solder, a thermally andelectrically conductive adhesive, or a thermally conductive andelectrically non-conductive adhesive, to the central pad 410. It will beappreciated that in those embodiments in which the central pad 410 forbonding the LED die 240 is not electrically conductive, the central pad410 can be merely a region on the floor of the cavity rather than apatterned layer of some material on the floor of the cavity. In otherwords, the die attach layer 245 bonds the LED die 240 directly to thefloor of the cavity in the central pad region.

The central pad 410 is surrounded on three sides by three bonding pads430, 440, and 460, each connected to one of the remaining three partialvias 290, 292, and 296. An electrical contact (not shown) on the topsurface of the LED die 240 is wire bonded to one of these three bondingpads 430, 440, and 460 where exposed on the floor of the cavity 250(i.e., within the circle 270). The four partial vias 290, 292, 294, and296 connect the bonding pads 430, 440, and 460 to external electricalcontacts (not shown) on either the top of layer 210 or the bottom oflayer 230, or both. These external electrical contacts provide leads toa power source on a circuit board. It can be seen from FIGS. 2-4 thatafter the package 200 is fully assembled most of the metallizationpattern shown in FIG. 4A is sandwiched between layers 230 and 220 andhidden from view.

In the embodiment shown above in FIG. 4A, the central pad 410 servesboth as an electrical connector and a thermal bonding pad between theLED die 240 and the top surface of the thermal conduction layer 230. Tofacilitate electrical connection, the LED die 240 may be either directlybonded to the central pad 410 or attached thereto using an electricallyconductive adhesive. In this disclosure, an adhesive is considered to beelectrically conductive if it has a volume resistivity less than 1×10⁻²ohm-meter. For better performance, an electrically conductive adhesivedesirably should have a volume resistivity less than 1×10⁻⁴ ohm-meter.It should be understood, however, that in some embodiments the centralpad 410 serves as a thermal bonding pad but not as an electricalconnector, as described elsewhere herein. In such embodiments, thecentral pad 410 is not connected to one of the partial vias 290, 292,294, and 296. Instead, all partial vias 290, 292, 294, and 296 areconnected to a respective side pad (such as the side pads 430, 440, and460).

FIG. 4B illustrates another exemplary metallization pattern for the topsurface of thermal conduction layer 230 of the LED package 200 of FIGS.2 and 3. In this embodiment a first pad 470 is connected to two partialvias 292, 294, and a second pad 480 is connected to the other twopartial vias 290, 296. An exemplary spacing between the first and secondpads 470 and 480 is 0.10 mm. Nickel, tungsten, and silver are exemplarymetals for the metallization. In some embodiments, silver is coated overanother metal, such as nickel. Line 490 indicates where the bottomsurface of the LED die 240 is bonded to the first pad 470. One benefitof the exemplary metallization pattern of FIG. 4B, compared to themetallization pattern shown in FIG. 4A, is that a greater area of thefloor of the cavity within the inner diameter 270 is metallized, whichserves to reflect a greater amount of light upward and out of thepackage.

FIG. 5 illustrates an exemplary metallization pattern for the bottomsurface 235 of the thermal conduction layer 230. In this embodiment, acentrally located pad 510 provides a thermal path from the bottom 520 oflayer 230 to a substrate (not shown) to which the package 200 isattached. The substrate can include a heat sink. The pad 510 is circularor square in some embodiments, but is not limited to any particularshape.

Each of the four partial vias 290, 292, 294, and 296 at the corners ofthe package 200 connect to one of the separate semi-circular electricalcontacts 530, 540, 550, and 560, respectively. One of the foursemi-circular electrical contacts, 550 in this particular embodiment, isconnected through one of the four partial vias (294 in this case) andtrace 420, as shown in FIG. 4A, to the central pad 410, while the otherthree semi-circular electrical contacts (530, 540, and 550 in thisembodiment) connect to the three bonding pads 430, 440, and 460,respectively. Thus, when attached to the substrate, the centrallylocated pad 510 is soldered (or otherwise bonded, such as with athermally conductive epoxy) to the substrate for heat dissipation andtwo of the four semi-circular electrical contacts 530, 540, 550, and 560are connected to electrical contacts on the substrate to provide anelectrical path through the LED package 200 and to the LED die 240. Oneof the two semi-circular electrical contacts (550 in this embodiment)connects through the central pad 410 to the bottom of the LED die 240,while the other (any one of 530, 540, and 560) is connected through itsrespective side bonding pad (430, 440, and 460) to the top of the LEDdie 240 by a wire bond (not shown). The particular semi-circularelectrical contact 530, 540, or 560 that is used to connect to the LEDdie 240 is determined according to the characteristics and therequirements of the particular LED die 240.

It will be understood that by having an arrangement of several bondingpads in a number of different locations enables the same package to beused with different LED designs. Thus, an LED from one manufacturer maybe bonded to one set of bonding pads while an LED from anothermanufacturer may be bonded to another set of bonding pads. In thisrespect the package is universal to different LEDs from differentsources. Further still, the design of the package of the presentinvention allows for flexible and simple processes for attaching LEDs tothe packages.

In alternative embodiments, the top surface 280 of the top body layer210 has a metallization pattern to provide electrical contacts ratherthan the bottom surface of the thermal conduction layer 230. Each of thepartial vias 290, 292, 294, and 296 at the corners and sides of the LEDpackage 200 connect to a separate electrical contact on the top surface140 of the top body layer 210. In these embodiments wire bonds to theelectrical contacts on the top surface 140 of the top body layer 210connect the LED package 200 to a power source or a circuit board.Locating the electrical contacts on the top of the package 200 ratherthan the bottom provides a greater area of contact between the bottomsurface 235 and the substrate for even greater heat dissipation. The LEDpackage 200 in these embodiments can be bonded to a substrate, forexample, by solder or thermally conductive epoxy. The bond does not haveto be electrically conductive.

It will be appreciated that the packages of the present disclosureprovide improved heat dissipation in several ways, some of which arelisted as follows. In some embodiments, the use of a material havingsuperior thermal conductivity for the thermal conduction layer 230improves heat dissipation. In other embodiments, the accommodation foran electrically nonconductive material for thermal conducting makes itpossible to use unconventional thermally conductive materials, forexample AlN ceramic, to form the thermally conducting layer. In otherembodiments, optimizing the thickness of the thermal the conductinglayer 230 further improves heat dissipation. In still other embodiments,providing a large area of contact between the bottom surface 235 ofthermal conduction layer 230 and the substrate to which it attaches canfurther improve heat dissipation. In some embodiments, the packages ofthe present disclosure also direct a greater percentage of light out ofthe package, both reducing the heating of the package from absorbedlight and increasing the light production efficiency.

Because of the improved heat dissipation, exemplary packages accordingto the present disclosure exhibit thermal resistances of about 6° C./Wat an output greater than 1 watt per package. Exemplary packagesaccording to the present disclosure with four LED dice exhibit a thermalresistance of 3° C./W, with outline dimensions of 7 mm×7 mm×1 mm. Thepresent disclosure also makes highly compact LED packaging possible. Insome exemplary packages, the square LED package has a width and lengthof about 4.4 mm and a thickness of about 1 mm (with thicknesses of about0.5 mm, 0.1 mm and 0.3 mm for the top body layer, the intermediate bodylayer and the thermally conducting layer, respectively). The presentdisclosure therefore enables high-power LEDs to be used inhigher-temperature environments, such as in automotive enginecompartments, as well as in applications where high-temperaturecomponents cannot be tolerated, such as in dental applications, forexample, in an illumination device used to cure dental cements.

The features disclosed in the present disclosure can be combined withother techniques of LED packaging. For example, the package of thepresent disclosure can further use encapsulating techniques as describedin the U.S. patent application Ser. No. 11/036,559, entitled “LightEmitting Device with a Thermal Insulating and Refractive Index MatchingMaterial,” filed on Jan. 13, 2005, which is incorporated by referenceherein.

FIG. 6A is a cross-sectional view of another exemplary embodiment of theLED package of the present disclosure. From top to bottom, the LEDpackage 600 comprises layers 610, 620, and 630. Similar to the LEDpackage 200 of FIG. 2, layer 610 is a top body layer, layer 620 is anintermediate body layer, and layer 630 is a thermal conducting layer. AnLED die 640 mounted to a top surface of thermal conducting layer 630through an LED die attach layer 645. A thermal insulation layer 650 anda luminescent layer 655 are placed in a tapered cavity having the shapeof an inverted cone. The cavity has a side wall extending from a top rim660 to a bottom rim 670. The LED package 600 also has an auxiliarymember 680 enclosing the package from the top. The auxiliary member 680is optional and can be, for example, an optical lens for focusing thelight emitted from the LED package 600. The auxiliary member 680 canalso serve as a protective capping layer.

It can be seen that the thermal insulation layer 650 is disposed betweenthe luminescent layer 655 and a top surface of the LED die 640. Thethermal insulation layer 650 at least partially protects the luminescentmaterial in the luminescent layer 655 from the heat produced by the LEDdie 640, thus, better maintaining thermal properties, such as lightconversion efficiency and output wavelength, at or near optimal valuesfar longer than under the prior art. The thermal insulating material ofthermal insulation layer 650 can also be a material with an index ofrefraction chosen to closely match that of the material of the LED die640.

The use of a thermal insulating material to protect the luminescentmaterial within the encapsulant member from the heat produced by the LEDis made particularly effective when applied in the LED packages of thepresent disclosure. It will be appreciated that prior art light emittingdevices do not include thermal insulation to protect phosphors from theheat generated by the LEDs because heat dissipation has been anoverriding concern in such devices. Put another way, designers of priorart light emitting devices have sought to dissipate as much heat aspossible through the phosphor-containing layers (e.g., luminescent layer655) because to do otherwise would require too much heat dissipationthrough the remainder of the light emitting device. However, where thethermally conducting layer 630 provides sufficient heat conduction, itis no longer necessary to conduct heat through the phosphor-containingluminescent layer 655, and thermal insulation can be introduced toshield the luminescent materials.

The thermal insulation layer 650 is preferably transparent, or nearlyso, to the light emitted from the LED die 640. The thermal insulatingmaterial is therefore preferably transparent to at least one wavelengthemitted by the LED die 640. The wavelengths emitted by various availableLEDs extend over a wide spectrum, including both visible and invisiblelight, depending on the type of the LED. The wavelengths of common LEDsis generally in a range of about 200 nm-2000 nm, namely from theinfrared to the ultraviolet.

In order to effectively thermally insulate the luminescent layer 655,the thermal insulating material of the thermal insulation layer 650should have a low thermal conductivity, desirably with a thermalconductivity of no more than 0.5 watt per meter per degree Kelvin (W/m°K), and more desirably with a thermal conductivity of no more than 0.15W/m° K. The thermal insulating material for the thermal insulation layer650 desirably also has high heat resistance, preferably with a glasstransition temperature, T_(g), above 170° C., and more preferably aglass transition temperature above 250° C. Furthermore, in order to havegood thermal compatibility and mechanical compatibility between thethermal insulation layer 650 and other components, especially the LEDdie 640, which are typically semiconductor materials, the thermalinsulating material desirably has a coefficient of thermal expansion nogreater than 100 ppm/° C., and more desirably a coefficient of thermalexpansion no greater than 30 ppm/° C.

Luminescent materials suitable for the present invention include bothfluorescent materials (phosphors) and phosphorescent materials.Phosphors are particularly useful for LED-based white light sources.Common phosphors for these purposes include Yttrium Aluminum Garnet(YAG) materials, Terbium Aluminum Garnet (TAG) materials, ZnSeS+materials, and Silicon Aluminum Oxynitride (SiAlON) materials (such as.alpha.-SiAlON).

The present invention also provides a light emitting device comprising apackage of the invention configured with an LED die and a luminescentmaterial. In one embodiment, light emitting device produces white lightbased on a monochromatic LED. This can be done, for example, by using avisible light LED and a compensatory phosphor, or by using an invisiblelight LED together with RGB phosphors. For instance, a blue LED-basedwhite light source produces white light by using a blue light LED and aphosphor that produces a yellowish light.

FIGS. 6B and 6C show cross-sections of additional embodiments of the LEDpackage 600. In FIG. 6B the top body layer 610 includes a circular notch685 to receive a lens 690. The lens 690 can be glass or plastic, forexample. The notch 685 beneficially provides a guide that centers thelens 690 over the LED die 640 during assembly. In some of theseembodiments, the top body layer 610 comprises a metal such as acopper-tungsten (Cu/W) alloy. The tapered cavity and the notch 685, insome of these embodiments, are formed by a stamping operation. Infurther embodiments, the intermediate body layer 620 and the thermalconducting layer 630 are also made of alumina.

In FIG. 6C the LED package 600 comprises an alignment layer 695 placedabove the top body layer 610. A circular aperture in the alignment layer695 creates essentially the same guide for the lens 690 as describedabove with respect to FIG. 6B. The alignment layer 695 can include, forexample, metal or ceramic. In those embodiments in which layers 610,620, and 630 include AlN, the alignment layer 695 can also include AlN.

The LED package of the present invention, in some embodiments, cansupport multiple LED dies within a single package to further increasethe output level and density. FIG. 7 is a top view of an LED package 700in accordance with another embodiment of the present disclosure. The LEDpackage 700 is similar to the LED package 200 in FIGS. 2-5, except thatthe LED package 700 contains multiple LEDs (710A, 710B, 710C, and 710D)instead of a single LED. The top view of the LED package 700 shows thecavity 730, the top surface 740, the outer diameter 760 and the innerdiameter 770 of the cavity 730, and the four partial vias 790, 792, 794,and 796. In the particular embodiment shown in FIG. 7, the LED package700 includes four LEDs 710A, 710B, 710C, and 710D, although in principleany other number of LEDs may be arranged in a package of the presentinvention. The four LEDs 710A, 710B, 710C, and 710D can be the same ordifferent, and in some embodiments are independently operable. Forexample, the multiple LEDs (710A, 710B, 710C and 710D) may beselectively operable and may be operable in any combination. The LEDpackage 700 is intended to provide an LED package capable of producingan output of 1-15 watts with a thermal resistance of 3° C./W, but is notlimited thereto.

Methods are disclosed for fabricating a layered LED package as describedwith reference to FIGS. 2-7. The methods vary depending upon thematerials selected for each layer, specific designs, such as the patternof metallization and the location and routing of the electricalconnections, and applications of the LED package. In those embodimentsshown in FIGS. 2-5 and in which all three layers 210, 220, and 230 aremade of a ceramic, for example, the layers 210, 220, and 230 can bemanufactured separately, stacked together, and co-fired (sintered) tobond the layers 210, 220, and 230 together. When non-ceramic materialsare used for layers 210 and 220, however, the layers 210 and 220 can bebonded together with suitable adhesives or solders.

In one embodiment of the method of the invention, multiple LED packagesare formed together in a batch process in which the individual LEDpackages are fabricated in parallel as a panel 800 from which individualLED packages can later be separated. FIG. 8 shows a top view of aplurality of LED packages 810 manufactured in parallel during anexemplary embodiment of a fabrication process. In this embodiment, theLED packages 810, which can be fabricated to include LED dies 820, areassembled in a square grid pattern separated by snap lines 830. Rows orcolumns of the packages 810 can be snapped apart along the snap lines830, and then further sub-divided into individual LED packages 810.According to this embodiment, each of the top body layer (e.g., 210),the intermediate body layer (e.g., 220) and the thermally conductinglayer (e.g. 230) for the plurality of LED packages 810 is produced as awhole piece, and each layer is independently fabricated as a sheet andthen bonded together. LED dies 820 can be added to the grid of LEDpackages 810 before the grid is separated into individual LED packages810.

Easily fractured materials, such as ceramics, are particularly suitedfor the above described embodiment. Separating the grid into theindividual LED packages 810 would be difficult if a metal, such ascopper, is used to form a bottom plate for heat dissipation. If amaterial that is not easily fractured is used for any of the threelayers (e.g., the top body layer 210, the intermediate body layer 220and the thermal conduction layer 230), it may be necessary to preparesuch layers along the snap lines 830 with deep grooves or perforationsto facilitate separation.

The grid in FIG. 8 also includes an array of vias (holes) 840 along thesnap lines 830. Each via 840 is shared by four neighboring LED packages810, except for those located at an edge or corner which would be sharedby either one or two neighboring LED packages 810. After the individualLED packages 810 are separated along the snap lines 830, the vias 840are separated apart to become partial vias (e.g., 290, 292, 294 and296).

To produce a thermally conducting layer (e.g., 230 or 630) using aceramic material according to a particular embodiment, for example, aceramic layer of a material such as AlN is prepared with a square arrayof vias 840 disposed therethrough. The vias 840 sit at the intersectionsof the snap lines 830 in FIG. 8. Ultimately, when the LED packages 810are separated from one another, each via 840 becomes a partial via(e.g., 290, 292, 294, and 296) of four different neighboring packages810. The top and bottom surfaces of the ceramic layer are patterned, inexemplary embodiments, with metallization as shown in FIGS. 4 and 5.Patterning can be achieved, for example, by plating. Suitable metals forthe metallization include tungsten and nickel. These patterns arerepeated for each package 810 that will be produced.

Various patterns of metallization may be used to achieve differenteffects and to suit the different requirements of the LED dies 820. Insome embodiments, for example, the central pad (e.g., the central pad410 in FIG. 5) serves both as a thermal contact and an electricalcontact. In these embodiments, the central pad on the top surface of thethermally conducting layer (230) is connected by a trace (420) to one ofthe partial vias (294) so that an electrical connection extends from thecentral pad to the opposite surface of the thermally conducting layer.If desirable, the electrical connection may be further extended to thecentral pad (510). In these embodiments, a small patch of AlN, oranother material, can be placed over the trace (420) between the centralpad and the partial via to prevent solder from flowing along the traceduring soldering.

To produce an intermediate body layer (e.g., layer 220), according tothis embodiment, a layer of a material such as AlN is prepared with asquare array of vias disposed therethrough. The square array of viasmatches the square array of vias in the thermally conducting layer.Additionally, a square array of apertures is defined in the layer suchthat each aperture is centered in a square defined by four adjacentvias. These apertures correspond to the inner diameter of the cavity(e.g., the inner diameter 270 in FIGS. 2-5) of the respective LEDpackage.

To produce a top body layer (e.g., layer 210), according to thisembodiment, a layer of a material such as AlN is prepared with a squarearray of vias disposed therethrough. The square array of vias matchesthe square arrays in the thermally conducting layer and the intermediatebody layer. Additionally, a square array of apertures is defined in thelayer such that each aperture is centered in a square defined by fouradjacent vias. The array of apertures on the top body layer match thearray of apertures on the intermediate body layer but have a differentdiameter. These apertures are preferably inclined or otherwise shaped toprovide a sidewall as discussed above with respect to FIGS. 1-3.Specifically, in a preferred embodiment, each inclined aperture has atop rim that corresponds to the outer diameter (e.g., the outer diameter260 in FIGS. 2-5) of the cavity in the respective LED package, and abottom rim that corresponds to the inner diameter (e.g., the innerdiameter 270 in FIGS. 2-5) of the cavity in the respective LED package810. The top body layer is then metallized to provide sidewallmetallization and any electrical contacts for the top surface. For theembodiments that do not require electrical contacts for the top surfaceof the top body layer, no electrical contacts are formed on the topsurface.

Once the thermally conducting layer, the intermediate layer and the topbody layer are individually prepared, the three layers are broughttogether in an assembly, the vias in each layer are aligned, and thethree layers are bonded together. As noted above, where all three layersare ceramic the assembly can be co-fired, else the layers can be bondedtogether with a suitable adhesive or solder. In the latter embodiments,the adhesive can serve to electrically insulate the metallization on thetop surface of the thermally conducting layer (e.g., metallizationpattern shown in FIG. 4A) from an intermediate layer comprising a metalsuch as copper. Once the layers have been bonded to one another, thevias 840 can be plated to provide electrical connections betweenmetallizations on the various surfaces of the layers.

Although the LED packages 810 can be separated at this point forsubsequent fabrication into light emitting devices, it is oftendesirable to first attach LED dies 820 to form an entire panel 800 oflight emitting devices in parallel. To create a panel 800 of lightemitting devices, solder flux or a thermally conductive die-attach isdispensed and the LED dies 820 are bonded to the LED packages 810. Then,each LED die 820 is wire bonded to the appropriate bonding pads.Preferably, the cavities of the LED packages 810 are next filled toencapsulate the LED dies 820. In some embodiments this process includesforming a thermally insulating layer over the LED die 820, forming aluminescent layer over the thermally insulating layer, and then forminga lens over the luminescent layer. Finally, the assembly is diced alongthe snap lines 830. It will be appreciated that the light emittingdevices of the present invention can be manufactured with fewerprocessing steps than prior art devices, in some instances fewer thanhalf as many steps.

To produce an embodiment such as that shown in FIG. 6C, in which aceramic alignment layer 695 is included, the method described above canbe modified so that the alignment layer 695 is co-fired together withthe thermally conducting, intermediate, and top body layers.Alternately, a metal alignment layer 695 can be bonded to the top bodylayer with a suitable adhesive or solder.

In those embodiments that include an alignment mechanism for aligning alens such as lens 690 in FIGS. 6B and 6C, the lens can be added to thepackage 810 in a number of different ways. In some embodiments, a vacuumtool is used to pick up a lens and move the lens into position. In otherembodiments a number of lenses are held on a strip of tape; a lens onthe tape is aligned with the package 810 and a tool presses the lensinto the guide to transfer the lens from the tape and-to the package810. It will be appreciated that lens transfer by vacuum tool or fromtape can be achieved either before or after the LED packages 810 areseparated from one another.

In an exemplary batch process that can be performed before the LEDpackages 810 are separated from the panel 800, the lenses are formed byinjection molding. In this process a mold having an array of lens-shapedwells is sealed to the panel 800 so that one well is aligned with eachof the packages 810. A suitable plastic is injected into the mold tofill the wells. The plastic is then cured to form the lenses. In anotherexemplary batch process, the lenses are formed by mask printing.

FIG. 9 depicts a method 900 according to an exemplary embodiment of theinvention. Method 900 comprises a step 910 of forming a panel, a step920 of defining a grid on a surface of the panel, an optional step 930of bonding an LED die within a cavity of the panel, and a step 940 ofseparating a unit from the panel by breaking the panel along lines ofthe grid. In those embodiments in which method 900 is directed toforming an LED package, step 930 is omitted and the resulting unit, theLED package, does not have an LED die. The LED die can be subsequentlyadded to the package to form a light emitting device. In thoseembodiments in which method 900 is directed to forming a light emittingdevice, the LED die is added to a cavity within the panel in step 930before the unit, in this case the light emitting device, is separatedfrom the panel in step 940.

The present disclosure further provides LED package structures and lensstructures that provide stronger attachments between the lenses and theLED packages. The improved attachment provides increased resistance toseparation of the lenses from the LED packages caused by mismatchedCTEs, or thermal effects such as adhesive degradation. The improvedattachment further provides resistance to separation due to mechanicalstresses to the devices, or due to shear forces between the lenses andthe LED packages. The present disclosure further provides methods forlens fabrication. The present disclosure also provides a method forapplying an adhesive layer between a lens and an LED package thatreduces internal reflection of light within the adhesive layer, whichincreases total luminosity and overall efficiency of the LED device.

FIGS. 10 and 11 show cross-sectional views of an LED package 1010 and alens 1050 of the present disclosure. FIG. 10 shows the lens 1050 and theLED package 1010 prior to assembly and FIG. 11 shows the lens 1050mounted on the LED package 1010. The LED package 1010 includes anencapsulated LED 1040, a socket 1020, and a top surface 1035. Theencapsulated LED 1040 is configured to emit light toward alight-emitting side of the LED package 1010. The socket 1020 is disposedon the light-emitting side of the LED package 1010 and is defined by asidewall 1025 and a socket floor 1030. The sidewall 1025 can be acontinuous surface around the periphery of the socket floor 1030 of thesocket 1020. The top surface 1035 is exterior to the socket 1020 and mayform a generally annular surface about the periphery of the socket 1020.

In some embodiments, the LED package 1010 includes various layers (e.g.,a thermal conducting layer, a thermal insulation layer, a luminescentlayer, protective capping layer, an intermediate body layer, a top bodylayer, etc.) as described elsewhere herein. As discussed with respect toFIG. 6C, an alignment layer with an aperture, such as the alignmentlayer 695, can be used to form the socket 1020.

The lens 1050 includes a cap 1060, a plug 1070, and a lower surface1065. In plan view, the lens 1050 can be circular, oval, rectangular, orvarious other shapes. In various embodiments, the cap 1060 is convex,concave, or various other shapes configured to focus, disperse, mask, orotherwise modify light emitted from the LED package 1010. Examples ofother shapes for the cap 1060 include an asymmetric shape, a Fresnelsurface, a collimating lens, etc. In some embodiments, the lens 1050 hasa mushroom shape. In some embodiments, the surface of the cap 1060 isconfigured to diffuse light exiting the lens 1050, for example using atextured surface.

The plug 1070 is configured to fit into the socket 1020 and includes asidewall 1075. The sidewall 1075 forms a continuous surface around theperiphery of the plug 1070. The plug 1070 mechanically stabilizes theattachment of the lens 1050 to the LED package 1010 and serves to resistshear forces between the lens 1050 and the LED package 1010 that canresult in the lens 1050 becoming loose and/or separating from the LEDpackage 1010. The lens 1050 can be secured to the LED package 1010 usinga press fit, a friction fit, or an interference fit between the sidewall1075 of the plug 1070 and the sidewall 1025 of the socket 1020.

The plug 1070 further provides additional bonding surfaces such as thelower surface 1065 and the sidewall 1075 for securing the lens 1050 tothe LED package 1010. For example, the lens 1050 can be secured to theLED package 1010 using an adhesive 1110 between the lens 1050 and theLED package 1010. In some embodiments, the adhesive 1110 is applied tothe top surface 1035 and bonds the cap 1060 to the LED package 1010.Alternatively, the adhesive 1110 can form a layer between the lens 1050and the LED package 1010. In some embodiments, the adhesive 1110 forms alayer that extrudes between the top surface 1035 of the LED package 1010and the cap 1060. While the cap 1060 is illustrated in FIG. 11 as havinga width 1080 that is less than a width 1085 of the LED package 1010, thewidth 1080 of the cap 1060 can be greater than the width 1085 of the LEDpackage 1010.

FIGS. 12 and 13 show cross-sectional views of an LED package 1210 and alens 1250 of the present disclosure. FIG. 12 is a cross-sectional viewof the LED package 1210 and the lens 1250 prior to assembly and FIG. 13is a cross-sectional view of the lens 1250 mounted to the LED package1210. The sidewall 1225 defines an angle “Φ” with respect to a socketfloor 1230, and a sidewall of the lens 1250 defines at an angle “13”with respect to a lower surface 1265. The angles Φ and β as illustratedin FIGS. 12 and 13 are about 135 degrees. However, the angles Φ and βcan include a range of angles. For example, the range of angles caninclude about 90 degrees to about 140 degrees. In some embodiments, theangle Φ is the same as the angle β. When the angles Φ and β are lessthan 90 degrees, the lens sidewall 1275 and the socket sidewall 1225 canform an interference or “snap” fit. While the lens 1250 is illustratedin FIG. 13 as having a width 1280 that is less than a width 1285 of theLED package 1210, width 1280 of the lens 1250 can be greater than thewidth 1285 of the LED package 1210.

FIGS. 14 and 15 show cross-sectional views of the LED package 1010 ofFIG. 10 and lens 1250 of FIG. 12. FIG. 14 is a cross-sectional view ofthe LED package 1010 and the lens 1250 prior to assembly and FIG. 15 isa cross-sectional view of the lens 1250 mounted to the LED package 1010.As discussed elsewhere herein, the angle β includes a range of angles,for example, greater than 90 degrees to about 140 degrees. The inclinedsidewall 1275 can accommodate horizontal misalignment between the lens1250 and the LED package 1010 during assembly of the lens 1250 with theLED package 1010. For example, the inclined sidewall 1275 can guide thelens 1250 into place in the socket 1020 when using vacuum handlingequipment to place the lens 1250, as discussed elsewhere herein. Whilethe lens 1250 is illustrated in FIG. 15 as having a width 1280 that isless than the width 1085 of the LED package 1010, width 1280 of the lens1250 can be greater than the width 1085 of the LED package 1010.

Air bubbles in a transparent, adhesive layer between the LED package1010 and the lens 1050 can reduce the transparency of the adhesivelayer. The number of air bubbles can be reduced by depositing anadhesive bead having a preferred shape and size on the LED package 1010.FIGS. 16-19 illustrate successive stages of bonding a lens 1050 to anLED package 1010. FIG. 16 is a cross-sectional view of an adhesive bead1610 applied to an LED package 1010 before attaching the lens 1050. Theadhesive bead 1610 is characterized by a convex bead surface 1620, awidth 1630, and a height 1640. In some embodiments, the width 1630 ofthe adhesive bead 1610 is in a range of about 30 percent to about 50percent of a width 1650 of the socket 1020. In some embodiments, theheight 1640 of the adhesive bead 1610 is in a range of about 20 percentto about 35 percent of the width 1630 of the adhesive bead 1610. In someembodiments, the viscosity of the adhesive bead 1610 is in a range ofabout 2000 to 4000 centipoise.

The adhesive 1110 can be transparent to light in wavelengths emitted bythe encapsulated LED 1040 and/or emitted by a luminescent layer withinthe LED package 1010. In some embodiments, the adhesive includesluminescent material and/or forms a luminescent layer. Other examples ofadhesive properties include, an electrically conductive epoxy, a solder,a solder mixed with glass beads, a thermally conductive and electricallynon-conductive epoxy, or a nano-carbon-fiber filled adhesive. Suitableadhesives include silicone, epoxy, etc. In some embodiments, a preformedring including solder mixed with glass beads can be disposed on the topsurface 1035 and form a hermetic seal between the LED package 1010 andthe lens 1050, or between the LED package 1210 and the lens 1250, orbetween the LED package 1010 and the lens 1250.

FIG. 17 is a cross-sectional view of the lens 1050 in contact with theadhesive bead 1610. In FIG. 17, the lower surface 1065 of the lens 1050is illustrated making initial contact with the adhesive bead 1610 at apoint at or near an apex of the convex bead surface 1620. FIG. 18 is across-sectional view of the lens 1050 applying a force to the adhesivebead 1610. The force “F” spreads the adhesive bead 1610 across the lowersurface 1065 of the lens 1050 and the socket floor 1030 of the LEDpackage 1010. Surface tension of the adhesive bead 1610 can combine withwetting of the lower surface 1065 of the lens 1050 (and the socket floor1030 of the LED package 1010) to maintain the convex shape in the convexbead surface 1620 thereby reducing the likelihood of trapping airbubbles in the adhesive material.

FIG. 19 is a cross-sectional view of an assembled light-emitting device1900 including an adhesive layer 1910 between the lens 1050 and the LEDpackage 1010. Excess adhesive material can form an adhesive fillet 1920around the periphery of the lens 1050 as illustrated. While FIGS. 16-19illustrate bonding a lens 1050 including a plug 1070 to an LED package1010 including a socket 1020, in some embodiments, other mating surfacesmay be used for the lens 1050 and the LED package 1010. For example, thelens 1050 can include a generally flat surface that omits the plug 1070and the LED package 1010 can include a generally flat surface that omitsthe socket 1020.

As discussed elsewhere herein, a lens can be formed by injectionmolding. In this process a mold having a lens-shaped well is sealed toan LED package having a socket. A suitable material, e.g., a plastic ina fluid state, is injected into the mold to fill the well and thesocket. The injected material is then cured to form the lens. Theprocess can be performed as a batch process on an array of LED packages,using a mold having an array of lens shaped wells.

FIGS. 20-21 illustrate successive steps in fabricating a lens using aninjection mold. FIG. 20 is a cross-sectional view of a mold 2010 sealedto an LED package 1210 prior to injection of a fluid lens material. Themold 2010 includes an injection port 2020 configured to admit the lensmaterial such as a plastic, silicone, or epoxy, configured to cure to asolid shape. The LED package 1210 and the mold 2010 combine to form aninjection mold.

FIG. 21 is a cross-sectional view of a completed LED device including amolded lens 1250 after the mold 2010 has been separated from the LEDpackage 1210. The sidewall of the LED package 1210 is inclined at anangle Φ. The angle Φ between the sidewall 1225 and the socket floor 1230is illustrated as less than 90 degrees, which provides an inferencebetween the lens 1250 and the LED package 1210. However, the angle Φ caninclude other angles, for example a range from about less than 90degrees to about 140 degrees. The angle Φ is illustrated in FIGS. 20 and21 as being fabricated using molding techniques. However other methodsof fabrication can be employed to achieve an angle Φ less than 90degrees.

Another method of manufacturing a lens includes forming a lens blank andthen machining the blank to remove excess material. For example, a glassblank can be turned to remove material to form the plug. FIG. 22 is across-sectional view of an exemplary embodiment of a lens blank 2210prior to machining, and FIG. 23 is a bottom plan view of the lens blank2210. FIG. 24 is a front elevation illustrating the resulting lens 1050.In some embodiments, the lens blank 2210 is formed by molding, e.g.,injection molding. Alternatively, the lens blank 2210 can be cast. Invarious embodiments, the lens blank 2210 is fabricated from materialsincluding glass, plastic, silicone, epoxy, etc.

The lens blank 2210, as illustrated, is a hemisphere having radialsymmetry. Other suitable shapes having radial symmetry include acircular cylinder, a spherical section, a concave spherical section,etc. A plug 1070 is formed by removing the material in an annular volumedefined by a region 2220 as illustrated in FIGS. 22 and 23. The lensblank 2210 in FIG. 22 includes a region 2220 of material, which can beremoved to fabricate the lens 1050 from the lens blank 2210. When thelens blank 2210 has radial symmetry, the material can be removed byturning the lens blank 2210. Alternatively, the material in the region2220 can be removed by grinding. In other examples, when the lens blank2210 does not have radial symmetry, the material in the region 2220 canbe removed, for example, by using an endmill.

FIGS. 25-26 show bottom plan views illustrating alternative shapes forthe lens 1050. FIG. 25 illustrates a generally oval shape for the lens1050. The oval shape for lens 1050 has a diameter D1 in a minor axis,and a diameter D2 in a major axis. The diameter D2, as illustrated, isgreater than the diameter D1. In some embodiments, the ratio of thediameter D1 to the diameter D2 is about 3 to 4, reflecting an aspectratio of a standard television screen. In another embodiment, the ratioof the diameter D1 to the diameter D2 is about 9 to 16, reflecting anaspect ratio of a wide screen television. Other ratios of the diameterD1 to the diameter D2 can be employed. Moreover, the lens 1050 can befabricated in other shapes of varying complexity, for example a hexagon.The lens 1250 can also be described by shapes similar to thoseillustrated in FIGS. 22 and 23 including an allowance for the inclinedsidewall 1275.

FIG. 26 illustrates a generally rectangular shape for the lens 1050,having a width “W” and a length “L.” In some embodiments, the ratio ofthe width “W” to the length “L” is about 3 to 4, reflecting an aspectratio of a standard television screen. In another embodiment, the ratioof the width “W” to the length “L” is about 9 to 16, reflecting anaspect ratio of a wide screen television. Other ratios of the width “W”to the length “L” can be achieved. In various embodiments, the aspectratio of the lens 1050 and/or shape of the cap 1060 can be configured toshape a beam light, for example, for use in a projector or a headlightof an automobile.

FIG. 27 depicts an exemplary method 2700 for fabricating alight-emitting device. The method 2700 comprises a step 2710 ofproviding an LED package with a socket, a step 2720 of providing a lensincluding a plug and a cap, an optional step 2730 of depositing anadhesive in the socket, and a step 2740 of attaching the lens to the LEDpackage. In those embodiments in which the method 2700 is directed tomechanically securing the lens in an LED package, the step 2730 isomitted and the resulting light-emitting device does not include anadhesive layer.

FIG. 28 depicts a method 2800 for fabricating a lens. The method 2800comprises a step 2810 of forming a lens blank, and a step 2820 ofmachining the lens blank to form the lens. In some embodiments, the lensblank is formed from glass, and the lens blank is turned to removematerial from an annular region to form the plug.

FIG. 29 depicts a method 2900 for molding a lens. The method 2900comprises a step 2910 of providing an LED package with a socket, a step2920 of placing a mold over the socket, a step 2930 of introducing afluid material into the mold, and a step 2940 of curing the fluidmaterial into a shape of the lens.

FIG. 30 depicts a method 3000 for forming an adhesive layer between alens and an LED package. The method 3000 comprises a step 3010 ofintroducing a bead of adhesive onto the LED package, a step 3020 ofcontacting a point on the bead of adhesive with the lens, and a step3030 of spreading the adhesive using the lens. Although FIGS. 10-26illustrate lenses having a plug and FIGS. 10-21 illustrate LED packageshaving a socket it will be understood that an adhesive layer may beformed between other mating surfaces using the method 3000. For example,a lens and an LED package may each include a substantially flat matingsurface.

In the foregoing specification, the present invention is described withreference to specific embodiments thereof, but those skilled in the artwill recognize that the present disclosure is not limited thereto.Various features and aspects of the above-described invention may beused individually or jointly. Further, the present invention can beutilized in any number of environments and applications beyond thosedescribed herein without departing from the broader spirit and scope ofthe specification. The specification and drawings are, accordingly, tobe regarded as illustrative rather than restrictive. It will berecognized that the terms “comprising,” “including,” and “having,” asused herein, are specifically intended to be read as open-ended terms ofart. It will be further recognized that “LED” and “LED die” are usedinterchangeably herein.

What is claimed is:
 1. A method of fabricating a light-emitting device,the method comprising: providing a package including an encapsulated LEDconfigured to emit light toward a light-emitting side of the package,and a socket disposed on the light-emitting side of the package;providing a lens including a plug and a cap; depositing an adhesivewithin the socket; and attaching the lens to the light-emitting side ofthe package, such that the plug is disposed within the socket.
 2. Themethod of claim 1, wherein providing the lens comprises machining a lensblank to form the plug of the lens.
 3. The method of claim 2, whereinmachining the lens blank comprises turning the lens blank.
 4. The methodof claim 3, wherein the lens blank comprises glass.
 5. A method offabricating a light-emitting device, the method comprising: providing apackage including an encapsulated LED configured to emit light toward alight-emitting side of the package, and a socket disposed on thelight-emitting side of the package; placing a mold over the socket, themold defining a shape of a cap; flowing a material into a space formedby the mold and the socket; and curing the material.
 6. The method ofclaim 5, wherein the material comprises plastic.
 7. The method of claim5, wherein the material comprises silicone.
 8. A method of attaching anLED lens to an LED package to form a light-emitting device, the methodcomprising: introducing a bead of adhesive having a convex surface and aviscosity of about 2000 to 4000 centipoise onto a surface of the LEDpackage; contacting a point on the convex surface of the bead ofadhesive with a surface of the LED lens; and spreading the adhesivebetween the surface of the LED package and the surface of the LED lens.9. The method of claim 8, wherein the contacted point on the convexsurface of the bead of adhesive is at about an apex of the convexsurface of the bead of adhesive.
 10. The method of claim 8, wherein awidth of the bead of adhesive is between about 30 percent to about 55percent of a length of the surface of the LED package.
 11. The method ofclaim 8, wherein a height of the bead of adhesive is between about 20percent to about 35 percent of a width of the bead of adhesive.
 12. Themethod of claim 8, wherein the bead of adhesive includes silicone.